W3C home > Mailing lists > Public > www-rdf-logic@w3.org > June 2002

Re: Implementing statement grouping, contexts, quads and scopes (was: Re: Out of context, in context, out of subject ????)

From: pat hayes <phayes@ai.uwf.edu>
Date: Tue, 25 Jun 2002 11:28:08 -0500
Message-Id: <p05111b0bb93e49539457@[]>
To: Patrick Stickler <patrick.stickler@nokia.com>
Cc: www-rdf-logic@w3.org

>On 2002-06-21 15:53, "ext Jonathan Borden" <jonathan@openhealth.org> wrote:
>>  The concept of "dark triples" as a layering option seems to be getting a bit
>>  misunderstood. The essence of "dark" or "unasserted" triples is simply that,
>>  from a technical perspective, it is difficult (some would indeed say
>>  impossible) to define a language such as OWL (and given the constraints
>>  placed on this language by the WebOnt charter etc.) in RDF if OWL is to have
>>  the characteristics we desire, and RDF triples are all "truths".
>I consider RDF to already have a mechanism for expressing unasserted
>triples, namely reification.

No. reification doesn't do that. Reification *describes* triples. Of 
course that doesnt assert them, but it also does not express them. 
The difference can be seen very clearly by considering the daml:List 
vocabulary, which is used by DAML to construct lists in RDF triple 
graphs. A reification of a daml:List is not itself a daml:List, and 
would not work to encode DAML syntax. However, it would be better for 
DAML if it RDF could be prevented from asserting its list vocabulary.

>The only reason folks want to create something
>else, IMO, is simply because the RDF/XML syntax is so obese.

No, that isn't the primary reason. It is because reification means 
something different.

This whole topic was done to death about 18 months ago in this list, 
lets not go over it again.

Pat Hayes

>  I.e.
>    <rdf:Statement>
>       <rdf:subject   rdf:resource="#foo"/>
>       <rdf:predicate rdf:resource="&owl;bar"/>
>       <rdf:object    rdf:resource="#bas"/>
>    </rdf:Statement>
>It seems to me that the solution is simply to add a contracted form
>of reification, to make the existing mechanism more palatable. E.g.
>    <rdf:Statement rdf:about="#foo">
>       <owl:bar rdf:resource="#bas"/>
>    </rdf:Statement>
>Yes, this is a (minor) change to RDF/XML parsing, but IMO a far
>cheaper cost than any of the other proposals on the table for
>signaling "dark" triples. Note that it does not constitute a
>change to the RDF syntax, only to the special interpretation
>of rdf:Statement in contracted rather than full form. I.e it's
>only a change to the RDF/XML parsing algorithm. And since all
>RDF parsers are going to *have* to be revised to support the
>already adopted changes to RDF/XML, this is not a big deal.
>What more does OWL (or any other layer) need? An OWL application is
>then free to treat unasserted RDF statements employing OWL predicates,
>as asserted at the OWL layer, without any impact at all to RDF-only
>applications and without requiring RDF-only applications to know
>anything about any higher layers or (most importantly) needing to
>explicitly know which predicates in otherwise RDF asserted triples
>are "dark" and must actually be treated as unasserted at the
>RDF layer (what nonsense).
>Patrick Stickler              Phone: +358 50 483 9453
>Senior Research Scientist     Fax:   +358 7180 35409
>Nokia Research Center         Email: patrick.stickler@nokia.com

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Received on Tuesday, 25 June 2002 12:28:11 UTC

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